Means of preserving metallic surfaces



252. COMPOSITIONS,

Patented Nov. 5, 1929 UNITED STATES hummus;

JAMES C. VIGNOS, OF NITRO, WEST VIRGINIA, ASSIGNOR TO THE RUBBER SERVICE LABORATORIES 00., OF AKRON, OHIO, A CORPORATION OF OHIO MEANS OF PRESERVING METALLIC SURFACES No Drawing.

The present invention relates to the cleaning and preservation of a metallic surface wherein the surface is in contact with liquids of an acid nature. More particularly, the invention relates to the prevention of excessive to attack unclean portions of metallic surfaces.

In the art of pickling, metal is treated with dilute acids to remove rust and scale from the metal surface after which the metal is washed with water and dipped into an alkaline bath to remove the last traces of free acid. The acid solution removes the rust and scale, but unfortunately from the pickling standpoint it also attacks the clean portions of the metal, thereby causing pitting or overpickling of portions of the metallic surface. Such pitting is particularly detrimental and undesirable when the metal is to be plated, painted or galvanized, cold worked and the like.

By means of the present invention, the objectlonable features of the pickling process are substantially overcome and eliminated. To accomplish this in accordance with the present invention, there is added to the pickling bath or other acid solution employed, a regulating agent or ingredient which acts to rest-rain the action of the acid in attacking the metal or in other words, the solution se- 5 lectively removes oxides and the like without materially attacking the free metal.

The regulators or inhibitors which are disclosed in the present application comprise the reaction products of the aldehyde ammonias 40 and thioureas or derivatives thereof.

The invention will be readily understood from the following description and examples. In the example set forth for carrying out the metal pickling process, conditions were imposed which duplicated, so far as pos- Application filed April 18,

1928. Serial No. 271,119.

sible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed. The heating of the metallic test strips in the pickling liquor in the manner a hereinafter set forth was, however, from three to four times as long as that ordinarily followed in commcrcial practice for the acid concentrations employed.

The test pieces of steel were approximately three inches square, cut from sheets having a carbon content of 0.04% and 0.12% respectively a hereinafter stated. Tests were also made in which pieces of open hearth steel approximately three inches square were used. These pieces of steel were immersed in about 500 cc. of a sulfuric acid solution containing approximately 8% of 66 Baum acid and a small quantity of one of the preferred type of inhibitors. Although the quantity of inhibitor used may vary between relatively wide limits, it has been found that particularly favorable results are realized when the proportion of inhibitor is from 0.001 to 0.1 of 1% of the weight of the acid solution employed. However, the amount of inhibitor used may, if necessary or desirable, be increased to that quantity which forms a saturated solution of the acid solution employed.

The test pieces were subjected to the action of the pickle liquor for approximately one hour at a temperature of approximatel rom 176 to 185 F. to C.). For 15 acid concentration, it is commercial practice to pickle at approximatel between to F. (66 to 88 C), for rom fifteen to twenty minutes. In all cases the results were compared with similar tests wherein the steel or iron test pieces were subjected under the conditions set forth to the action of an acid solution of the strength specified above but containing no inhibitor. Comparisons of the loss in weight suffered by the various test pieces give at once a measure of the inhibiting action exerted by the compounds tested.

One example of the preferred type of inhibitors was prepared in the following manner. ldeh d e ammonia was prepared by any convement methdd, for example by cooling approximately 333 cc. of denatured alcoho to substantially 0 C. and then adding approximately 88 parts of acetaldehyde (two molecular proportions) in small portions, keeping the temperature below 15 C. Approximately 34 parts of ammonia (two molecular proportions?J was then passed into the solution, prefera ly at a temperature below 15 C. Approximately 228 parts of thiocarbjtnilidlone molecular proportion) we en added and the mixture stirred at refluxing temfiiail re for a period of approximately thi eelmprs. At the end of this period the reaction was complete, as no more ammonia was given off.

The reaction taking place ma sented most conveniently accor following equation:

be repremg to the grams per square inch of surface exposed as compared with a loss of .0145 grams per square inch where no inhibitor was employed.

A similar test was made in which two test pieces of steel, each approximately three inches square and containing 0.12% of carbon, were immersed in about 500 cc. of sulfuric acid solution containing approximately 8% of 66 Baum acid and about 0.01 grams of the reaction roduct of acetaldehyde ammonia mhificarbanilid'fifiabout sixty minu "l'fiiaintaining the solution at a temperature of from 80 to 85 C. The loss in weight of the test strips resulting from the pickling treatment was found to be only about 1.7% of the lossthat resulted when similar test pieces were pickled under the same conditions in an acid solution containing no inhibitor.

Tests. made in which 0.02 ams of the re: action-prodgct of acetaldehy e ammonia and unsymmetrically substituted thioureas, for

can

\MQHJ Other reaction products of various aldehydeammonias and thioureas were phpiired in a similar man'ner."

An alternative method of preparing the preferred type of compounds comprises the addition of the solid aldehyde ammonia to the mixture of the thiourea and alcohol, or other solvent.

The reaction product of aldehyde ammonias and thioureas hereinbefore stated as effective for preventing excessive deterioration of metals immersed in or subjected to the action of an acid solution have been employed in the following manner.

A solution was prepared for use in pickling metals comprising about 500 cc. of sulfuric acid containing approximately 8% of 66 Baum acid and about 0.01 grams of the reaction product of acetaldehyde ammonia and thiocarbanilid added. The resulting solution contained about 0.002% by weight of the said reaction product. Iron test strips containing 0.04% carbon were then immersed in the solution for about sixty minutes while maintaining the solution at a temperature of from 80 to 85 C. The loss in weight of the test strips resulting from the pickling treatment was found to be only about 4.8% of the loss that resulted when a similar test strip was pickled under the same conditions in an acid solution containing no inhibitor. In other words, the inhibitor increased by about 20/21 the metal loss due to solvent action of the acid on the metal. When this loss was calculated on the surface exposed to the solution, it was found to amount to 0.0007

avl'

example phgny l- -tolyl-thi0urea, were used as inhibitors, yie ddd 'a isult showing that the solvent action of the acid on the metal containing 0.04% carbon was decreased about 16/17. The loss of metal per square inch of surface exposed to the acid solution was .00092 grams as compared with a loss of .0158 grams per square inch of surface exposed when no inhibitor was employed.

As a further example of the preferred type of inhibitor, a test was made in which an acid solution of the strength mentioned contained 0.004% b Weight of the reaction roduct of acetalidehyde am fionia and t iolrreai- 'such a solution was found to pickleiron and steel strips containing 0.12% carbon in such a manner that the metal loss was found to be about 11.7% of the loss that resulted when similar test pieces were pickled under the same conditions in an acid solution containing no inhibitor.

A similar test was carried out in which the reaction product of acetaldeliydre ammonia afi'ddioithotomflhourems used as an inhibtttrm aaa solution of the strength mentioned and containing approximately 0.004% by weight of the inhibitor was found to pickle steel strips containing 0.04% carbon in such a manner that the loss was found to be -.00077 grams per square, inch, as compared to the loss of .0158 ams per uare inch of exposed surface w ere no inhi itor was used.

Other examples, wherein an acid solution of the strength mentioned and which contained approximately 0.004% by weight of 252. COMPOSITIONS,

the preferred type of inhibitor, are shown in the following table. In these examples the steel test pieces contained 0.04% carbon.

Loss of weight per square Inhibitor inch or surface exposed Reaction product of hexamethylenetetramine and thio- Grams carbanil' 00 i Reaction product of hexamethylene-tetramine and (11-0- tolyl-thiourea. 0012 Reaction product. of crotonaldehydeammonia and thiocarbanilid .00034 Reaction product of crotonaldehyde-amrnom'a and 111-0- 1 tolyl-thiourea 00069 F Reaction product of crotonaldehydeammonia and phenyl-o-to yl thiourea 00080 Reaction product of (urfuralamide and thiocarbanilid. 00100 5 Reaction product of (uriulalamide and phenyl-o-tolylthiourea 00077 Reaction product of benzaldehydeammonia and thiocarbanilid 00106 Reaction product of benzaldehydcammonia and phenylo-tolyl-thiourea 00122 Reaction product of benzaldehydeammonia and triphenylguanyl-thiourea 00144 No inhibit/or 01577 As another example of the inhibitory effect of the preferred type of compounds, a test piece of open hearth steel was immersed in an acid solution of the strength mentioned and containing approximately 0.002% by weight of the reaction product of acetaldehyde ammonia and thiocarbanilid. The loss of metal per square inch of surface exposed was 0.00119 grams as compared with a loss of 0.0788 grams per square inch of surface exposed where no inhibitor was employed.

It is evident from the various examples hereinbefore set forth that the reaction products of the aldehyde ammonias and the thioureas comprise a class of effective inhibitors in processes wherein metals are subjected to the action of an acid. Greater inhibiting action has been found to be produced by the use of a larger quantity of the various compounds than that set forth in the examples. It is not desirable, however, to use a greater quantity of inhibitor than will completely dissolve in the solution employed.

The examples hereinbefore set forth are to be understood as illustrative only and not at all limitative of the scope of the invention. Other examples of the process described are apparent to those skilled in the art to which the invention pertains, wherein metals other than the one particularly described may be similarly treated or wherein difi'erent acids or different acid concentrations may be employed, or the periods of treatment may be varied or different temperatures employed. The invention is to be considered as limited solely by the .followin claims wherein the invention is claimed as roadly as possible in view of the prior art.

What is claimed is:

1. The process of cleaning a metal surface which comprises treating such metal with a sulfuric acid solution containing a small pro- Examine portion of the reaction product of an aldehyde ammonia and a thiourea.

2. The process of cleaning a metal surface which comprises treating such metal with a sulfuric acid solution containing a small proportion of the reaction product of an aldehyde ammonia and a substituted thiourea.

3. The process of cleaning a metal surface which comprises treating such metal with a Sulfuric acid solution containing a small proportionof the reactionproduct of an aldehyde ammonia and an aryl substituted thiourea.

4. The process of cleaning a metal surface which comprises treating such metal with a sulfuric acid solution containing a small proportion of the reaction product of an aldehyde ammonia and a thiocarbanilid.

5. The process of cleaning a metal surface which comprises treating such metal with a sulfuric acid solution containing a small proportion of the reaction product of an aliphatic aldehyde ammonia and thiocarbanilid.

6. The process of cleaning a metal surface which comprises treating such metal with a sulfuric acid solution containing a small proportion of the reaction product of acetaldeyde and thiocarbanilid.

7. A metal-treating compound comprising a sulfuric acid solution containing the reaction product of an aldehyde ammonia and a thiourea.

8. A metal-treating compound comprising a sulfuric acid solution containing the reaction product of an aldehyde ammonia and a substituted thiourea.

9. A metal-treating compound comprising a sulfuric acid solution containing the reaction product of an aldehyde ammonia and an aryl substituted thiourea.

10. A metal-treating compound comprising a sulfuric acid solution containing the reaction product of an aldehyde ammonia and thiocarbanilid.

11. A metal-treating compound comprising a sulfuric acid solution containing a small proportion of the reaction product of acetaldehyde ammonia and thiocarbanilid.

12. The process of cleaning a metal surface which comprises treating such metal with a sulfuric acid solution containing a small proportion of the reaction product of an aldehyde ammonia and a symmetrically di-aryl substituted thiourea.

13. A metal-treating compound comprising a sulfuric acid solution containing the reaction product of an aldehyde ammonia and a symmetrically di-aryl substituted thiourea.

In testimony whereof I hereunto afiix my signature.

JAMES C. VIGNOS. 

